Rapid Diversification and Time Explain Amphibian Richness at Different Scales in the Tropical Andes, Earth’s Most Biodiverse Hotspot

Abstract

The Tropical Andes make up Earth's most species-rich biodiversity hotspot for both animals and plants. Nevertheless, the ecological and evolutionary processes underlying this extraordinary richness remain uncertain. Here, we examine the processes that generate high richness in the Tropical Andes relative to other regions in South America and across different elevations within the Andes, using frogs as a model system. We combine distributional data, a newly generated time-calibrated phylogeny for 2,318 frog species, and phylogenetic comparative methods to test the relative importance of diversification rates and colonization times for explaining Andean diversity at different scales. At larger scales (among regions and families), we find that faster diversification rates in Andean clades most likely explain high Andean richness. In contrast, at smaller temporal and spatial scales (within family-level clades within the Andes), diversification rates rarely explain richness patterns. Instead, we show that colonization times are important for shaping elevational richness patterns within the Andes, with more species found in habitats colonized earlier. We suggest that these scale-dependent patterns might apply to many other richness gradients. Recognition of this scale dependence may help to reconcile conflicting results among studies of richness patterns across habitats, regions, and organisms.

BAMM gives misleading rate estimates in simulated and empirical datasets

“…We have observed results suggesting this pattern in our own analyses (Hutter et al. ). Given this, studies that have found negative results using BAMM (e.g., nonsignificant relationships) should be viewed with particular caution.…”

Diversification rates of the “Old Endemic” murine rodents of Luzon Island, Philippines are inconsistent with incumbency effects and ecological opportunity

“…Thus, geographic scale and isolation likely influence the mechanism by which diversification occurs, as has been suggested in the tropical Andes (Hutter et al. ). Despite the limited space afforded to colonists of Luzon compared to continental radiations, the patterns of LOE diversification were more consistent with a mechanism of allopatric speciation, where species diversity is able to accumulate nearly constantly, offset slightly by background extinction rates.…”

Why is fruit colour so variable? Phylogenetic analyses reveal relationships between fruit‐colour evolution, biogeography and diversification

“…Jansson & Davies, ; Pyron & Wiens, ; Rolland, Condamine, Jiguet, & Morlon, ), especially high‐elevation tropical habitats (e.g. Hughes & Eastwood, ; Hutter, Guayasamin, & Wiens, ; Hutter et al, ). However, in our results (Table ), the best‐fitting model to explain variation in diversification rates includes violet colour alone.…”

“…We speculate that certain fruit colours may be favoured in environments that promote rapid diversification (e.g. montane tropical regions; Hughes & Eastwood, ; Hutter, Lambert, & Wiens, ; Spriggs et al, ). Thus, fruit colour itself may not directly drive diversification, but there might be a synergy between fruit colour and geographic distribution that affects diversification.…”